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Coordination Compounds Class 12 Notes Chemistry Chapter 5

Ligands: an ion or molecule capable of donating a pair of electrons to the central atom via a donor atom.

  • Unidentate ligands: Ligands with only one donor atom, e.g. NH3, Cl-, F- etc.
  • Bidentate ligands: Ligands with two donor atoms, e.g. ethylenediamine, C2O42-(oxalate ion) etc. 
  • Tridentate ligands: Ligands which have three donor atoms per ligand, e.g. (dien) diethyl triamine.
  • Hexadentate ligands: Ligands which have six donor atoms per ligand, e.g. EDTA. 

Chelating Ligands: 

  • Multidentate ligand simultaneously coordinating to a metal ion through more than one site is called chelating ligand. Example: Ethylenediamine (NH2CH2CH2NH2)
  • These ligands produce a ring like structure called chelate.
  • Chelation increases the stability of complex.
    Coordination Compounds Class 12 Notes Chemistry Chapter 5

Werner’s Theory:

  • Metals possess two types of valencies i.e. primary (ionizable) valency and secondary (nonionizable) valency.
  • Secondary valency of a metal is equal to the number of ligands attached to it i.e. coordination number.
  • Primary valencies are satisfied by negative ions, while secondary valencies may be satisfied by neutral, negative or positive ions.
    Coordination Compounds Class 12 Notes Chemistry Chapter 5
  • Secondary valencies have a fixed orientation around the metal in space.

[Co(NH3)6]Cl3
Primary Valencies = 3 Cl-
Secondary Valencies = 6 NH3
Coordination Sphere =  [Co(NH3)6]3-

Nomenclature of Complexes:

  • Positive ion is named first followed by negative ion.
  • Negative ligands are named by adding suffix - o.
  • Positive ligands are named by adding prefix – ium.
  • Neutral ligands are named as such without adding any suffix or prefix.
  • Ligands are named in alphabetical order.
  • Name of the ligands is written first followed by name of metal with its oxidation number mentioned in roman numbers in simple parenthesis.
  • Number of the polysyllabic ligands i.e. ligands which have numbers in their name, is indicated by prefixes bis, tris etc,
  • Number and name of solvent of crystallization if any, present in the complex is written in the end of the name of complex.
  • When both cation and anion are complex ions, the metal in negative complex is named by adding suffix-ate.
  • In case of bridging ligands:
    [Name of the groups to the left of bridging ligand (Oxidation state)] –μ – [Name of the groups to the right of bridging ligand (Oxidation state)] – [Name of negative ion]
Ligands
Name
Negative
CH3COO-
Acetato
CN-
Cyano
Br-
Bromo
Cl-
Chloro
F-
Fluoro
OH-
Hydrido
N3-
Nitrido
C2O42-
Oxalato
SO32-
Sulfito
O2-
Superoxo
O22-
Peroxo
O2-
Oxo
NH2-
Imido
SO42-
Sulphato
S2O32-
Thiosulfato
HS-
Mercapto
Positive
NO+
Nitrosonium
NH2NH3+
Hydrazinium
Neutral
H2O
Aqua
NH3
Ammine
CO
Carbonyl
CH3NH2
Methylamine
NO
Nitrosyl
C5H5N
Pyridine

Isomerism in coordination compounds
Coordination Compounds Class 12 Notes Chemistry Chapter 5

Structural Isomerism

  • Ionization Isomerism: Exchange of ligands between coordinate sphere and ionization sphere
    [Pt(NH3)4Cl2]Br2   & [Pt(NH3)4Br2]Cl2
  •  Hydrate Isomerism: Exchange of water molecules between coordinate sphere and ionization sphere
    [Cr(NH3)3(H2O)3]Br3   &  [Cr(NH32)3(H2O)2 Br]Br2 H2O   
  •  Linkage Isomerism: Ambient legend binds from the different binding sites to the metal atom.
    K2[Cu(CNS)4]  & K2[Cu(SCN)4
  • Coordination Isomerism: Exchange of the metal atom between coordinate sphere and ionization sphere when both are complex ions.
    [Cr(NH3)6][CoF6] & [Co(NH3)6][CrF6].
  • Ligand Isomerism: Different isomers of the same ligands attached to the metal.
    [Co(pn)2Br]Cl2 & [Co(tn)2Br]Cl2 Where,
    pn = 1,2- Diaminopropane
    tn = 1,3-Diaminopropane.

Stereoisomerism:
a.Geometrical Isomerism: When two similar ligands are on adjacent position the isomer is called cis isomer while hen they are on opposite positions, the isomer is called trans isomer.
Coordination Compounds Class 12 Notes Chemistry Chapter 5
b.Optical Isomerism: In order to show optical isomerism, the complex should form a non superimposible mirror image which rotates the place of polarized light in opposite direction.

Valence Bond Theory:
Hybridization:
Find out the hybridization of central metal ion using following steps:

  • Write down the electronic configuration of metal atom.
  • Find out oxidation state of metal atom.
  • Write down the electronic configuration of metal ion.
  • Write down the configuration of complex to find out hybridization.
  • Strong field ligands cause the pairing of electrons.
    Strong Field Ligands: CO, CN-, NO2-, en, py, NH3.
    Weak Filed Ligands: H2O, OH-, F-, Cl-, Br-,I -

When the d orbital taking part in hybridization is inside the s and p orbital taking part in hybridization with respect to the nucleus, it is called an inner orbital complex.
Example: d2sp3 hybridization of [Co(NH3)6]3+  involves 3d, 4s and 4p orbital, hence it is an inner orbital complex.
When the d orbital taking part in hybridization outside the s and p orbital taking part in hybridization with respect to the nucleus, it is called an outer orbital complex.
Example: sp3d2 hybridization of [CoF6]3- involves 4d, 4s and 4p orbital, hence it is an inner orbital complex.

Geometry:

Coordination Number
Hybridization
Geometry
4
sp3
Tetrahedral
dsp2
Square Planar
6
d2sp3 & sp3d2
Oct

Magnetic Properties:

  • Diamagnetic: All the electrons paired.
  • Paramagnetic: Contains unpaired electrons.

Spin:

  • Spin paired: All electrons paired.
  • Spin free: Contains unpaired electrons.

Colour:
Compound must contain free electrons in order to show colour.

Crystal Field Theory:
Strong field ligand causes greater repulsion and thus results in the formation of low spin complexes by pairing of electrons.

  • Weak field ligands result in the formation of high spin complexes
  • Order of strength of ligands: CO > CN- > NO2- > en > py = NH3 > H2O > OH- > F> Cl- > Br- >I-
    Coordination Compounds Class 12 Notes Chemistry Chapter 5
  • Octahedral Complexes: eg orbital are of higher energy than t2g orbital.
    Coordination Compounds Class 12 Notes Chemistry Chapter 5
  • Tetrahedral Complexes: eg orbitals are of lower energy than t2g orbitals.
    Coordination Compounds Class 12 Notes Chemistry Chapter 5 

 Δt = (4/9) Δo

Crystal Field Stabilization Energy:

System
High Spin
Low Spin
 
Electronic Configuration
CFSE
Electronic Configuration
CFSE
Octahedral Complex
d4
t2geg1
-(3/5)Δ0
t2g4 eg0
-(8/5)Δ0+P
d5
t2g3 eg2
0
t2g5 eg0
-(10/5)Δ0+2P
d6
t2g4 eg2
-(2/5)Δ0+P
t2g6 eg0
-(12/5)Δ0+3P
d7
t2g5 eg2
-(4/5)Δ0+2P
t2g6 eg1
-(9/5)Δ0+3P
Tetrahedral Complexes
d4
eg2  t2g2
-(2/5)Δt
eg4 t2g0
-(12/5)Δt +2P
d5
eg2  t2g3
0
eg4 t2g1
-2 Δt +2P
d6
eg3  t2g3
-(3/5)Δt +P
eg4 t2g2
-(8/5)Δt+2P 

Magnetic Properties: Complexes with unpaired electrons are paramagnetic while with no unpaired electron are diamagnetic.

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FAQs on Coordination Compounds Class 12 Notes Chemistry Chapter 5

1. What are coordination compounds?
Ans. Coordination compounds are complex molecules that consist of a central metal ion or atom bound to one or more surrounding ligands. These ligands are typically electron-rich species, such as molecules or ions, that donate electron pairs to the metal ion, forming coordinate covalent bonds.
2. How are coordination compounds named?
Ans. Coordination compounds are named using a specific set of rules. The name typically starts with the name of the metal followed by the names of the ligands, which are listed in alphabetical order. The ligands are named using special prefixes, such as "di-" for two ligands, "tri-" for three ligands, and so on. Additionally, the charge of the metal ion may be indicated using Roman numerals in parentheses.
3. What is the significance of coordination compounds?
Ans. Coordination compounds have various applications and significance. They are commonly used in medicine, as many metal-based coordination compounds exhibit biological activity and can be used as therapeutic agents. Additionally, coordination compounds are utilized in catalysis, materials science, and environmental studies. They also play a crucial role in biological processes such as oxygen transport in blood.
4. How do coordination compounds form coordination bonds?
Ans. Coordination bonds in coordination compounds form through the interaction between the metal ion and the ligands. The metal ion has empty orbitals that can accept electron pairs from the ligands, resulting in the formation of coordinate covalent bonds. The ligands donate electron pairs to the metal ion, establishing a stable complex.
5. What are the different types of ligands in coordination compounds?
Ans. Ligands in coordination compounds can be classified into several types. Some common ligands include monodentate ligands, which donate a single electron pair to the metal ion, and polydentate ligands, which can bind to the metal ion through multiple donor sites. Examples of polydentate ligands are ethylenediamine and EDTA. Ligands can also be classified as anionic, neutral, or cationic, depending on their charge.
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